It's a performance issue, yes; more or less all UE games run at 5-10 fps maximum, with a huge amount of heavy post-processing effects like bloom and motion blur. I couldn't find much info online on these issues sadly!
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I'll definitely be looking into this a lot more. I had some of my friends try it, and it seems to be definitely demanding on particular systems, but not due to the difference in hardware performance, but just hardware in general. I had someone with a lower tier rig running it fine while someone with a higher tier rig said they at one point were stuck at the same 5-10fps. Thanks for letting me know though, that's definitely frustrating!